Variegation in plants is defined as the normal green portion of the plant leaf being replaced by white, cream, yellow, or occasionally other colors, which may be in the form of blotches or stripes. The variegations can occur on the edge of the leaves (marginate variegation), or in the center of the leaf (medio variegation). Due to ornamental nature of variegated plants, these plants are desired by gardeners.
Variegations have been induced in plants by a variety of methods including the use of transposable elements (for example Itoh et al., 2002, Plant Cell Physiol. 43(5):578-8), plant transformation with variegated and distorted leaf (vdl) gene, located in the nucleus (Wang et al., 2000, Plant Cell. 12(11):2129-42), antisense glutamate 1-semialdehyde aminotransferase transformation, inhibiting chlorophyll synthesis with partial or complete suppression of the GSA-AT leading to severe plant damage (Hofgen et al., 1994, Proc Natl Acad Sci USA., 91:1726-1730), or spontaneous mutation in the nuclear genes that controlled organelle proteins or mutations in organelle genes (reviewed in Aluru et al., 2006, J. ExpBot. 57:1871-1881. Apuya et al., (2001, Plant Physiol. 126, 717-730) report that a T-DNA mutation in the chaperonin-60α gene (Cpn60) of Arabidopsis results in a defect in embryo development, causing developmental arrest before the heart stage.
Leaf bleaching, along with other abnormal phenotypes such as stunted growth, delayed flowering, reduced root development and the like have been observed in transgenic tobacco plants that constitutively express Arabidopsis Cpn60β transcripts in sense and antisense orientation (Zabaleta, E, et al. 1994, Plant Journal, Vol. 6, pp. 425-432).
Chaperonins are multi-subunit double-ring oligomeric proteins found in bacteria, mitochondria, and plastids. Chaperonins are abundant constitutive proteins that increase in amount after stresses, such as heat shock, bacterial infection of macrophages, and an increase in the cellular content of unfolded proteins.
Higher plant chloroplasts contain a 21-kDa protein, chaperonin 21 (Cpn21) (Hirohashi T. et al, Biochem Biophys Acta. 1999 1429(2):512-5). The chloroplast Cpn21 polypeptide consists of two Cpn10-like domains fused together in tandem. The cDNA sequence of the Cpn21 (AtCpn21) precursor protein from Arabidopsis thaliana is known, and the deduced amino acid sequence of the AtCpn21 precursor protein, 253 amino acids long, shows 61% identity with the spinach Cpn21 protein. The AtCpn21 precursor protein contains a typical chloroplast transit peptide of 51 amino acids at its amino terminus and two Cpn10-like domains, with these two domains exhibiting 46% sequence identity. The predicted, mature polypeptide of AtCpn21 was expressed in Escherichia coli as a soluble 21-kDa protein. Gel-filtration and chemical cross-linking analyses showed that the recombinant mature AtCpn21 protein forms a stable homo-oligomer composed of three or four polypeptides.
Hanania et al., 2007 (Transgenic Res. 16 :515-525) disclosed that Cpn21 was differentially disclosed in seeded and seedless grapes, and may have a role in seed abortion in some plants.
Sjogren et al., (2004, Plant Physiol, 136: 4114-4126), disclose Arabidopsis clpC1 T-DNA insertion mutants that lack on average 65% content of a stromal molecular chaperone (ClpC). Mutants display a retarded-growth phenotype, leaves with a homogenous chlorotic appearance throughout all developmental stages. Photosynthetic performance was impaired in knockout lines, with relatively fewer photosystem I and photosystem II complexes, but no changes in ATPase and RuBisCO content.